This invention relates to print cylinders used for screen printing and the like, and particularly to a novel extruded segment cylinder construction.
Print cylinders for screen printing et al are typically cast in sections from metal stock and joined by tie bolts into a solid unitary structure containing intricate features which must be individually machined into the cylinder for providing vacuum channels, end bearings and the like. Then, the cylinder must be given an overall lathe turning to true up the periphery. Such a manufacturing process is very expensive. It results in a cylinder which is heavy and costly. The cast vacuum channel configuration is also limited in design and finish, resulting in a restricted flow of air therethrough. The cost is disadvantageous for obvious reasons. The weight is also disadvantageous because the rotating cylinder must be repeatedly stopped, then reversed, and finally rotationally restarted during printing operations. The weight of the cylinder inherently limits the printing speed because it limits the frequency of stop and start movements as well as the position accuracy of the stopped cylinder.
It is also common practice in the screen printing field to employ a cylinder which has vacuum ports on its periphery for holding sheet stock being printed. Such cylinders have air flow passages which sequentially cause the vacuum ports to first pull a vacuum on the underside of the sheet stock and then release the vacuum, all as the cylinder rotates, see e.g. U.S. Pat. No. 2,606,492 to J. A. Black, column 5 et seq. and the figures relating thereto. However, the structure of the prior cylinders to achieve this action is complex and expensive to fabricate.